Generally, a process for synthesizing metallocene comprises converting cyclopentadiene or its derivative into an anion, complexing the resultant anion with a metal chloride, then separating and purifying the product to obtain a pure metallocene compound.
U.S. Pat. No. 5,200,537 discloses a process for preparing a metallocene having the general formula of (RC.sub.5 H.sub.4).sub.2 MX.sub.2, wherein R is C.sub.1 .about.C.sub.20 alkyl or silyl, M is zirconium or titanium, X is halogen. The process does not cost for refrigeration as it is carried out at room temperature, which comprises the preparation procedures of: (a) reacting Na(C.sub.5 H.sub.5) with RX(alkyl halide) in an organic solvent to form a mixture of RC.sub.5 H.sub.4 and C.sub.5 H.sub.5 ; (b) removing out the most of C.sub.5 H.sub.5 by vacuum stripping at room temperature; (c) protonating the RC.sub.5 H.sub.4 and (d) adding TiCl.sub.4 or ZrCl.sub.4 to form the metallocene compound, and then adding a solvent to separate out the pure metallocene compound. The yield is 56.about.74%.
In U.S. Pat. No. 5,336,795, a process is disclosed for preparing a transition metal complex compound having a mono-substituted cyclopentadiene ligand, wherein the mono-substituted cyclopentadiene ligand is prepared by using an oxide or hydroxide of alkali metal or alkali earth metal as a protonating agent, then the mono-substituted metallocene compound is formed by reacting the resultant ligand with a halide of transition metal elements.
In U.S. Pat. No. 5,001,205, a process for preparing a supported catalyst system of metallocene-aluminoxane is disclosed in detail, but no preparation process of the metallocene is given. The bridge-linked or noubridge-linked cyclopetadiene or a derivative thereof is used as a ligand of the metallocene, and is a pure metallocene compound. The aluminoxane used is methyl aluminoxane. The catalyst system is used for catalyzing the polymerization of ethene and of ethene with other .alpha.-olefins.
In EP 426,643 A.sub.1, a process is disclosed in detail for preparing a isopropyl bridge-linked fluorenyl cyclopentadienyl zirconium dichloride. The process comprises two steps, (i), reacting butyl lithium or methyl lithium with a metallocene ligand in a polar solvent, e.g. tetrahydrofuran, then removing out the solvent to obtain a solid powder reactant; and (ii) reacting the solid powder reactant with ZrCl.sub.4 powder at room temperature to carry out a solid-solid phase reactin in hexane, then removing out the solvent and washing the remainder to obtain a mixture of the isopropyl bridge-linked fluorenyl cyclopentadienyl zirconium dichloride and LiCl. The mixture can be used as a catalyst for preparing polypropylene. However, the mixture has poor stability and has to store in dry and oxygen-free conditions.
Furthermore, in CN 1 140 720A, a patent application of the present applicants, a composite metallocene catalyst with syndiotactic selectivity is disclosed. The catalyst prepared according to tile patent application is an three-constituent adduct of diphenylmethylene-(cyclopentadienyl-9-fluorenyl) zirconium dichloride.diethylether.lithium chloride having the expression of Ph.sub.2 C[Cp-9-Flu]ZrCl.sub.2.Et.sub.2 O.2LiCl, which is used as a catalyst mainly for preparing syndiotactic polypropylene.
In regard to the preparation method of the metallocene catalyst used as a main catalyst component for the polymerization of olefins in the prior art, significant defects include: (1) many steps and complicated reactions are involved in the preparation process, thus not only a number of reactors are needed, but also the related reaction conditions are needed to be controlled severely; (2) complicated processes for the separation and purification are needed in the preparation methods, such as recrystallization and the like; (3) generally, the stability of the purified metallocene compound in air is poor, so it is not easy to be stored for a long term of time; (4) in general, the yield is about 60%, because of many reactions and separation steps. Even in the disclosed preparation process in CN 1,140,720A of the present applicants, a three-constituent adduct of Ph.sub.2 C[Cp-9-Flu]ZrCl.sub.2.Et.sub.2 O.2LiCl can be directly prepared and used as catalyst without any complicated separation and purification steps, it is only suitable for use as a catalyst for preparating syndiotactic polypropylene since the metallocene compound is of a bridge-linked type and its ligand has a large steric effect. When the metallocene adduct having syndiotactic selectivity, after having been supported, is used for catalyzing the polymerization of ethene, the usage amount of the cocatalyst used with the main catalyst component, methyl aluminoxane(MAO) is high. When the ratio of AL/Zr is at about 500, the catalytic activity is high, but when AL/Zr ratio is down to less than 200, the catalytic activity will be greatly decreased, thus the application of the adduct in polymerization of ethene largely restricted. Furthermore, since the process having several steps for preparating the metallocene ligand is complicated and the yield in each step is about 50%, the total yield based on the initial reactants is very low, when, for example, di-phenyl-fluorenyl-cyclopentadienyl methane is prepared.
Therefore, an object of the present invention is to provide a three-constituent adduct of metallocene with high stability on the basis of the prior art mentioned above, being able to he easily prepared, and having overcome defects of the prior art.
The second object of the invention is to provide a process for directly preparing the abovesaid adduct in high yield without the complicated steps of separating and purifying the metallocene compound.